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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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302                                ALASKAN GLACIER STUDIES
side shows a flat tidal terminus extending a short distance out into the fiord, where Gilbert says there was none in 1899. The extreme southern edge of the ice cliff was a black, crevassed precipice, the lateral moraine of 1899 having been pushed forward into the sea.
Bryn Mawr Glacier. Bryn Mawr Glacier (PI. CXVHI), the largest independent cascading glacier in College Fiord, is over 3 miles long and varies in width from f of a mile to a mile. It is fed by two large tributaries which unite 2040 feet above sea level, coming from cirques at the level of about 4500 feet. Below the lip of the main hanging valley, 1S41 feet above sea level, the slope of the glacier averages 3700 feet to the mile. Above this level the slope flattens to the junction of the tributaries, each of which plunges down from a secondary hanging valley at a level of about 2500 feet. At the base of the steepened valley slope the glacier forms a slightly expanded piedmont bulb, and the lower | of a mile has a very low, flat surface grade. As in the Smith Glacier, there are no well defined lateral moraines, but a strong medial moraine extends from the junction of the tributaries to the sea. The glacier discharges more icebergs than any of the other cascading tongues and terminates with a precipitous cliff over 100 feet high.
Gilbert states that the Bryn Mawr Glacier "next south of the Smith, is somewhat larger. Its two main branches, gathering in mountain valleys not well seen from the sea, became visible in twin cascades, and then, uniting their streams, make a second leap to the sea. As tide is reached, there is a tendency to flatten the profile, and the central portion of the stream becomes nearly or quite horizontal for a few hundred feet before breaking off in the terminal cliff."
This shows clearly that the expanded lower portion with a flat foot, was already developed in 1899 and photographs by Grant and Paige prove this condition to have continued in 1905 and 1909. There was a narrow barren zone on either margin in 1899 and probably in 1905. Grant has stated that "a comparison of the photographs taken in 1899 with those taken in 1909 indicates that the glacier was farther advanced at the latter date and that its front (especially the southern half of the front) deployed more widely on the shallow bottom of College Fiord, A photograph taken in 1905 and an impression four years later indicates that the glacier was less advanced at the earlier date, and that it was then (1905) at approximately the same position as in 1899. Any close estimate of the actual amount of this advance (as recorded in the photographs taken in 1909) is impracticable from the data at hand, but it is probably as much as 500 feet." His photographs show an extensive gravel beach still bordering the southern half of the ice front in July, 1909.
There was very considerable advance between July, 1909, and July, 1910, for a photograph from Grant's site on College Point shows a lateral spreading of several scores of feet on both north and south margins of the glacier. That there has also been pronounced forward movement is evident by comparing the conditions in July, 1910, with a photograph taken by the Harriman Expedition in 1899. In this interval, the Bryn Mawr Glacier had advanced several hundred feet, most of the advance apparently taking place during 1910.
On each side of the glacier a small stream emerges from the ice, and at the time of our visit the borders of the glacier were encroaching on these stream courses. All along its northern margin the Bryn Mawr Glacier was advancing into the forest, where it was Trilling spruces up to 5 inches in diameter, suggesting that the glacier had not been so large for